An image forming apparatus for forming an image by means of an electrophotographic printing method can form a high-definition image with an easy operation. It is also easy to keep the image forming apparatus in good condition. Accordingly, the image forming apparatus has been frequently used for, for example, a copying machine, a printer or a facsimile, and therefore has been in widespread use. A typical electrophotographic image forming apparatus includes (i) a photoreceptor drum for forming an electrostatic latent image, (ii) a developing device for developing an electrostatic latent image to form a toner image, (iii) a transfer device for transferring a toner image onto a sheet, and (iv) a fixing device for fixing a toner image onto a sheet.
In such an image forming apparatus, toner to be consumed is replenished after toner present in the image forming apparatus is completely consumed. Meanwhile, when the toner is replenished to the image forming apparatus, the toner is possibly scattered in the air, or hands of a supplier are possibly contaminated with the toner. This is because the toner is made up of very light fine particles. In order to prevent the toner particles from being scattered in the air, a toner cartridge that contains toner, which is configured to be detachable from the image forming apparatus and exchangeable as it is, has been frequently used. The toner cartridge is exchanged as follows. An empty cartridge is detached from an image forming apparatus, and a new cartridge is attached to the image forming apparatus. The empty cartridge is refilled with toner, and reused. Alternatively, since awareness about an environmental problem has been recently raised, material recycling in which the empty cartridge is not discarded but recycled as a resin material has been promoted.
However, the image forming apparatus from which the toner cartridge is detachable causes a problem that toner fluidity deteriorates and therefore it becomes difficult to supply toner from the toner cartridge to a developing device or to an intermediate toner hopper in a case where the toner cartridge is left in the image forming apparatus for a long period. In order to solve the problem, for example, Patent Literature 1 discloses a toner cartridge including a toner stirring member with a stirring blade in its toner container so that the toner fluidity is improved.